Brooks Glycerin 21 running shoe review

Brooks knows a thing or two about making running shoes, having been in the game since 1914. The Glycerin series offers a well-cushioned, stacked ride, perfect for longer road runs, but without making the shoe overly heavy.

Our tester is a fan of high energy-return and a thick, bouncy sole, and the Glycerin 21 ticked all their boxes, soon becoming a firm favorite. Having tested the Ghost 15 and Ghost 16 and not got on with them, the Glycerin 21 was a huge comeback for Brooks in our tester's eyes.

Brooks Glycerin 21: How we tested

Our reviewer initially tested these shoes several months ago and still uses them for road runs and treadmill work. Our tester has covered over 50km in these shoes, mostly over slow, long-distance runs.

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Brooks Glycerin 21: Build and cushioning

The Brooks Glycerin 21 is comparable to the Hoka Bondi 8 in terms of cushioning and support. Our tester tends to favor well-stacked, heavily-cushioned shoes that provide lots of bounce as they are a supinator (a natural gait pattern where the foot tends to roll outwards).

While this isn't a built-for-purpose stability shoe — for that you would need the Glycerin GTS 21 — the width of the sole means it is a very stable shoe that supports smooth heel-to-toe transitions. While with some shoes this can mean the inclusion of an invasive rocker, the Glycerin 21 feels very neutral underfoot.

The heel-to-toe drop of 0.39 in (10 mm) encourages the natural forward motion of the foot from heel to toe, and the 1.1 in (28 mm) heel stack height provides plenty of cushioning for heel-strike runners.

Brooks Glycerin 21: Design and upper

There is plenty of room in the toe box and the upper is soft and flexible, allowing for comfort when running on hard surfaces. The Brooks Glycerin 21 is super breathable, with an engineered warp-knit upper, which allows the feet to breathe, even on hot days.

The only downside is that this superior breathability means these shoes aren't at all waterproof.

Brooks Glycerin 21: Outsole

Our tester was particularly looking for a grippy outsole, having been let down by other Brooks shoes in the past. As a midfoot/forefoot-striking runner, they found other Brooks shoes — especially from the Ghost range — lacked grip in the toe area, leading to slipping.

While the Glycerin 21 is still designed for heel-strike runners, the outsole is grippy all the way through, making it suitable for those with a more forward footstrike pattern. Most recreational runners are heel-strike runners and the amount of cushioning in the crashpad provides ample protection.

Despite plenty of use, the outsole of our tester's pair of Glycerin 21s remains in good condition, with little wear to its deeply grooved pads.

Brooks Glycerin 21: Performance

The Brooks Glycerin 21 is a bouncy shoe, with a 2mm increased stack height compared to the previous generation. Despite this added height, it is 0.3 oz lighter than the Glycerin 20. However, it is still probably a little too heavy for those wanting to achieve speed PBs, as Brooks has prioritized comfort and cushioning over a light weight with the Glycerin range.

Brooks Glycerin 21: Verdict

The Glycerin 21 offers a robust, bouncy ride with lots of toe room and breathability.

If you are looking for a neutral shoe and aren't sure what to go for, the Glycerin 21 offers a more comfortable ride than the Ghost 16. For even more cushioning, the Glycerin Max is a more expensive and more stacked option.